The character is on the ground. An attacker who is prone has a -4 penalty on melee attack rolls and cannot use a ranged weapon (except for a crossbow). A defender who is prone gains a +4 bonus to Armor Class against ranged attacks, but takes a -4 penalty to AC against melee attacks. Standing up is a move-equivalent action that provokes an attack of opportunity.
If you are going to be a tripper, you need to argue with your DM about prone spellcasters. You see, this is the prone condition and it's a bit vague about a few things. So you need too figure out where your DM stands. Chances are you are going to want to trip a spellcaster at some point, and you are going to need to know what that spellcaster can do.
1)
Are Spells Ranged Weapons?The RAW of this doesn't say anything on this one. By strict RAW reading, you can cast ranged spells with no penalty when prone. Now to argue.
- Ranged Touch Attack Spells require an attack roll, just like projectiles and thrown weapons. If you need an attack roll and it is ranged, it clearly is a weapon.
- Nets are weapons and a ranged touch attack. Therefore, the fact that rays are touch attacks are not a reason to exclude them as weapons.
- The Weapon Focus Feat states, "Choose one type of weapon. You can also choose unarmed strike or grapple (or ray, if you are a spellcaster) as your weapon for purposes of this feat." Here we have it specifically listed that rays are "one type of weapon". So, we can conclude that rays (and thus ranged touch attacks) are considered "weapons". Since the only excluded weapon is Crossbow, we must assume that unless you can cast your ranged touch attack spells with a crossbow, that you cannot cast ranged touch attack spells while prone.
(As a DM, I would argue that wands are the equivalent to a Spell crossbow, and you can use a wand while prone just fine.)
Now, if you can get this past your DM, tripping a spellcaster limits them from a wide range of spells to ruin your day, to eliminating all ranged touch attacks, as well as imposing a -4 to hit roll on all melee touch attack spells.
(As a DM, I would rule that being prone has no effect on a spectral hand spell. That might seem obvious to some, but having checked other forums on the topic, I can see the need for clarification.)
2)
Is there a concentration check involved?Now, if you do manage to convince the DM that prone scorching ray casting is now off limits, what do you do about fireballs? (Remember, space is 3 dimensional. A wizard could cast the fireball high enough into the air to scorch anyone standing, but leave prone people unharmed. Something to keep in mind, oh prone wizard.) Well, for those sorts of spells, you have to convince the DM that lying on the ground requires a concentration check, if the spell in question has somatic components (Gestures)..
Now, by RAW, it doesn't. But, lets look at concentration checks more closely.
You must make a Concentration check whenever you’re distracted while engaged in an activity that requires your full attention. ... If you’re trying to cast, concentrate on, or direct a spell when the distraction occurs, add the level of the spell to the indicated DC.
Now, as one person asked else-forum, "If I'm lying on my back, how does that distract me from casting a spell? I can move my arms just fine."
Well, normally it wouldn't. But, if you are attempting to avoid getting hit during combat, one might assume that wiggling around on the ground avoiding sword blows is a "Vigorous Motion" or a DC 10 + (level of the spell you are casting) concentration check. By RAW, you can avoid blows just as well on your back as you can standing up. By RAI, can you truly say that it isn't distracting to roll around trying not to get hit?
Friend, fancy footwork don't work when you ain't on your feet.
So your argument is, if the Spellcaster is willing to forgo his Dex Bonus to AC, he isn't making any vigorous motion while lying on the ground and thus, no concentration check. But, trying to avoid sword blows while lying on the ground AND casting spells clearly IS vigorous motion, thus requiring a check. So if I knock down a spellcaster and he's trying to fireball me, it's a DC 10 + the spell he is trying to cast concentration check.
(As a DM, You'd be surprised how many Pre-Gen Spellcasting NPCs I've found with no concentration skill as a spellcaster. What? Do people just not play with concentration checks?)
3)
Does lying prone interfere with line of effect?This is the weakest of the three arguments, and won't come up very often, but it's something to keep in mind. It involves the cover rules.
Now, the cover rules are very subjective to begin with, so there is no real RAW way to answer this. It's a case by case situation. Keep it in mind and pull it out if you need to try and weasel out of something.
Now, lying on the ground does provide a +4 to AC from ranged attacks. This is the equivalent to normal, soft cover. No bonuses to reflex saves. No hide attempts. So, what happens if the target you are trying to reach is using cover as well?
Well, The argument goes, it would be additive. So if you are prone, and you are trying to hit a target behind normal cover, the combination is effectively improved cover, but he only has to deal with normal cover when attacking you. If your target has improved cover, it upgrades to total cover. You cannot hit him, while he can attack you.
After all, if you are looking out an arrow slit and plunking arrows into someone lying on the ground, how well is he going to be able to see you when he tries to return fire while attempting to avoid getting a sharpened bit of timber inserted into his left ventricle?
Like I said, it's subjective and entirely situational. But, I can see circumstances where you might want to go, "WAIT! The evil necromancer has been tripped and the prince he is trying to assassinate is hiding behind the throne! That's partial cover, but he's got a bad line of sight while lying on his back, so treat it as normal cover!"
Maybe the DM will buy it. Maybe the DM will roll his eyes and say, "It's 2 am in the goddamn morning! The Prince DIES. The necromancer DIES. Rocks fall, everybody DIES!"
In other words, don't be a dick about it, and use it only when it matters.
So, before deciding if you are going to specialize in tripping, be sure to iron out these consequences of lying prone for spellcasters before you make your PC. These three arguments can change being a tripper from being a spellcaster's worst nightmare, to being turned into a newt.